1. Field of the Invention
The present invention relates to a recording liquid such as print inks, marker inks, inkjet inks, electronic recording inks, non-aqueous paints, and liquid developers for use in electrophotography, electrostatic recording and electrostatic printing. In addition, the present invention also relates to an image forming method using the recording liquid (i.e., liquid developer).
2. Discussion of the Background
Electrophotographic developers are classified into dry developers and liquid developers. Liquid developers have an advantage over dry developers such that clear images can be produced because of including a toner having a finer particle diameter than that of the toner included in the dry developers.
Liquid developers are typically prepared by dispersing a resin, a colorant and a charge controlling agent in a non-aqueous solvent having a high electric resistance. The particle diameter of the toner dispersed in such liquid developers is typically from 0.1 to 2.0 xcexcm. In addition, liquid developers do not use an iron power carrier, which is typically used for dry developers and has a heavy weight, when images are formed, and therefore the liquid developers have the following advantages over dry developers:
(1) the stress applied to image forming apparatus is much less than that applied to image forming apparatus by dry developers; and
(2) high speed image recording can be performed.
As to the image fixing method for fixing an image formed by a liquid developer on a receiving material, the following fixing methods are well known:
(1) a fixing method in which an image is fixed by bringing the image into contact with a heat roller;
(2) a fixing method in which an image is fixed by being heated with hot air;
(3) a fixing method in which an image on a receiving material is fixed by bringing the backside of the receiving material into contact with a hot plate; etc.
In any one of the fixing methods mentioned above, the solvent in the liquid developer used is released into atmosphere. This is not preferable in view of environmental protection.
In attempting to prevent releasing of solvent vapors, Japanese Laid-Open Patent Publication No. (hereinafter referred to as JOP) 09-208873 discloses a fixing method in which an image formed by a liquid developer is fixed by being exposed to ultraviolet rays. However, the method has a disadvantage such that the image forming apparatus using the method becomes large in size.
JOPs 63-301966 to 301969, 64-50062 to 50067, 64-52167 and 64-142560 to 142561 have disclosed liquid developers for the image forming method using a heat fixing roller mentioned above. These liquid developers include an aliphatic hydrocarbon having a low boiling point as a main component of the carrier liquid. Therefore, the aliphatic hydrocarbon is released from the image forming apparatus into atmosphere. In addition, a silicone oil has to be applied to the heat fixing roller to prevent an offset problem in that a toner image adheres to the fixing roller. Therefore the image forming apparatus has problems in that the constitution of the image forming apparatus becomes complex and the number of consumable supplies (parts) increases.
In addition, liquid developers have a drawback in that adhesion of colorants included in the liquid developers to receiving materials is not satisfactory, resulting in poor fixation of the images on the receiving materials.
In inkjet recording methods, an ink drop is discharged from a recording head toward a receiving material to record an image on the receiving material, wherein the ink typically penetrates into the receiving material (i.e., the receiving material absorbs the ink). Such inkjet recording methods have the following advantages:
(1) images can be recorded quietly (with low noise);
(2) color images can be recorded at a relatively high speed; and
(3) plain papers can be used as the receiving material.
Therefore, recently the inkjet recording methods have been well used for image forming apparatus such as printers and facsimile machines.
As the ink for use in such inkjet recording methods, oil-based inks in which an oil-soluble dye is dissolved in an oil solvent, and aqueous inks in which a water-soluble dye is dissolved in an aqueous solvent are well known. The oil-based inks typically have the following advantages:
(1) images can be recorded on various receiving materials;
(2) recorded images are quickly dried (images quickly penetrate into receiving materials and can be absorbed by the receiving materials);
(3) recorded images have good water resistance; and
(4) the chance of occurrence of a clogging problem, in which a nozzle is clogged with the dye included in the inkjet ink used, resulting in occurrence of image omissions, can be reduced.
However, even such oil-based inks have a drawback in that the oil solvent tends to evaporate in a nozzle, and thereby the oil-soluble dye solidifies or aggregates in the nozzle, resulting in occurrence of a clogging problem. In addition, such oil-based inks typically include a solvent having a high boiling point. When such a solvent having a high boiling point is used, images having a high image density cannot be obtained (i.e., high quality images cannot be obtained).
As the marker ink, inks in which an oil soluble dye or pigment is dissolved or dispersed in an organic solvent having a relatively low boiling point are well known. As the organic solvent, aromatic solvents such as toluene and xylene are typically used. However, recently odor and toxicity of such aromatic solvents present a problem. Therefore, recently solvents having relatively low toxicity, such as alcohols, etyleneglycol monoalkyl ethers (i.e., Cellosolves), and propyleneglycol monoalkyl ethers are typically used as the main solvent of quick-drying marker inks.
Such marker inks typically include an oil-soluble dye selected from dyes listed in Color Index. For example, dyes prepared by mixing a leuco dye of a basic dye with an organic acid; dyes prepared by preparing a salt by reacting a basic dye with an acidic dye or a fatty acid; or dyes prepared by changing an acidic dye into an amine salt thereof, are typically used. These techniques have been disclosed in Japanese Patent Publication No. 49-19175 (method for manufacturing dye ink for felt pen); JOP 62-174282 (oil-based ink); JOP 62-207377 (oil-based marking ink composition); JOP 63-75068 (alcohol-soluble dye composition); and JOP 64-87677 (marking ink composition). However, these inks are not satisfactory in view of odor, writing property, preservability, and safety of human being.
Electronic recording inks are used for forming character and photographic images by moving particles of an ink upon application of an electric field thereto, wherein the ink includes ink particles dispersed in an insulating liquid and is contained in a container prepared by a transparent paper such as cellophane. The ink particles are small in size and charged, and therefore they can be moved upon application of a certain voltage thereto. However, the images exhibited by conventional electronic recording inks have poor contrast, and in addition the response of the electronic recording inks to application of a voltage is unsatisfactory.
Non-aqueous paints typically include a solvent such as toluene and xylene, and therefore the paints have a drawback in view of safety of workers handling the paints. Currently, non-aqueous paints which use an isoparaffin solvent have been developed and used, but the paints have drawbacks in that the resultant films have poor gloss and water resistance.
Because of these reasons, a need exists for a liquid developer which can be used for electrophotographic image forming methods and which can produce (color) images having high image density, high resolution and good color reproducibility while the evaporation amount of the solvent used therein is decreased. In addition, a need exists for a printing ink, a maker ink, and a paint, which have good preservability and which can produce images or coated films having good gloss and water resistance without causing a blurring problem. Further, a need exists for an inkjet ink which can produce images having good gloss and water resistance without causing a blurring problem and which hardly causes a clogging problem. Furthermore a need exists for an electronic recording ink which can exhibit images having good contrast while making improved response.
Accordingly, an object of the present invention is to provide a liquid developer which can produce color images having high image density, high resolution and good color reproducibility while the evaporation amount of the solvent used therein is decreased.
Another object of the present invention is to provide an inkjet ink which has good preservability and which can produce images having high gloss and good water resistance without causing blurred images and a clogging problem.
Yet another object of the present invention is to provide an electronic recording ink which makes quick response and can exhibit high contrast images.
A further object of the present invention is to provide a printing ink and a marker ink which have good preservability and can produce images having good gloss and water resistance without causing a blurring problem.
A still further object of the present invention is to provide a paint which has good preservability and which can produce a film having good gloss and water resistance.
A still further object of the present invention is to provide an image forming method which uses a liquid developer and by which color images having high image density, high resolution and good color reproducibility can be produced while the evaporation amount of the solvent used therein is decreased.
To attain such objects, the present invention contemplates the provision of a recording liquid (i.e., a printing ink (e.g., a stencil ink), an inkjet ink, a marker ink, an electronic recording ink, a paint and a liquid developer) including a carrier liquid and a colorant dispersed in the carrier liquid, wherein the carrier liquid includes at least one of a liquid paraffin and a linear silicone oil. The carrier liquid preferably includes both a liquid paraffin and a linear silicone oil. Within the context of the present invention, the term xe2x80x9clinear silicone oilxe2x80x9d indicates a silicone polymer having a substantial linear backbone containing less than 0.5% of non-linear (cyclic or branched) units, more preferably less than 0.2% of non-linear units, still more preferably less than 0.1% non-linear units, most preferably no non-linear units.
The liquid developer and paint of the present invention further includes a resin. The silicone oil preferably has a flash point not lower than 210xc2x0 C.
The liquid paraffin preferably has a flash point not lower than 130xc2x0 C. and a viscosity not less than 3 mPaxc2x7s at 40xc2x0 C.
The resin included in the liquid developer and paint preferably has a softening point of from 30 to 120xc2x0 C. The resin is preferably a resin selected from the group consisting of ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers and ethylene-acrylic ester copolymers.
The resin may be an epoxy resin having the following formula (1): 
wherein n is an integer of from 1 to 25; R1 represents a group xe2x80x94OOCkH2k+1, wherein k is an integer of from 1 to 30; R2 represents a group xe2x80x94CmH2m+1, wherein m is an integer of from 1 to 30.
The weight average molecular weight of the resin is preferably from 800 to 10000.
The colorant is preferably subjected to a flushing treatment using a resin which is preferably selected from the group consisting of ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers and ethylene-acrylic ester copolymers.
The ratio of the total weight of the resin and colorant to the total weight of the recording liquid is preferably not less than 10%.
The colorant (or toner) dispersed in the carrier liquid preferably has an average particle diameter of from 1 to 5 xcexcm.
The recording liquid preferably has a viscosity not less than 10 mPaxc2x7s at 25xc2x0 C.
In another aspect of the present invention, an image forming method is provided which includes the steps of:
applying the above-mentioned recording liquid (i.e., liquid developer) on a liquid bearing member such as rollers and belts to form a thin layer of the recording liquid on the liquid bearing member; and
developing an electrostatic latent image born on an image bearing member with the thin layer of the liquid developer to form a visual image on the image bearing member.
It is preferable that the image forming method further includes the step of subjecting the thin layer to corona-discharging before the developing step; and/or the step of applying a pre-wet liquid to at least the electrostatic latent image before the developing step. The pre-wet liquid is preferably the carrier liquid included in the liquid developer. The visual image is preferably transferred onto a receiving material via an intermediate transfer medium. The image bearing member is preferably a photoreceptor having both a water-repellant property and an oil-repellant property. The contact angle formed by the liquid developer and the photoreceptor having both a water-repellant property and an oil-repellant property is preferably not less than 30xc2x0.
These and other objects, features and advantages of the present invention will become apparent upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.